1. Field of the Invention
The present invention relates to an organic light emitting diode display and a driving method thereof, and more particularly, to an organic light emitting diode display and a driving method thereof, in which an image is displayed with uniform brightness.
2. Description of the Related Art
Various flat panel displays have recently been developed as alternatives to a relatively heavy and bulky cathode ray tube (CRT) display. The flat panel display includes a liquid crystal display (LCD), a field emission display (FED), a plasma display panel (PDP), an organic light emitting diode display (OLED), etc.
Among the flat panel displays, the organic light emitting diode display can emit light for itself by electron-hole recombination. Such an organic light emitting diode display has advantages in that response time is relatively fast and power consumption is relatively low. Generally, the organic light emitting diode display employs a transistor provided in each pixel for supplying current corresponding to a data signal to a light emitting device, thereby allowing the light emitting device to emit light.
FIG. 1 illustrates a conventional organic light emitting diode display.
Referring to FIG. 1, a conventional organic light emitting diode display includes a pixel portion 30 including a plurality of pixels 40 formed in a region defined by intersection of scan lines S1 through Sn and data lines D1 through Dm; a scan driver 10 to drive the scan lines S1 through Sn; a data driver 20 to drive the data lines D1 through Dm; and a timing controller 50 to control the scan driver 10 and the data driver 20.
The scan driver 10 generates scan signals in response to a scan control signal SCS from the timing controller 50, and supplies the scan signals to the scan lines S1 through Sn in sequence. Further, the scan driver 10 generates emission control signals in response to the scan control signal SCS, and supplies the emission control signals to emission control lines E1 through En in sequence.
The data driver 20 generates data signals in response to data control signal DCS from the timing controller 50, and supplies the data signals to the data lines D1 through Dm. At this time, the data driver 20 supplies the data signals corresponding to one horizontal line to the data lines D1 through Dm per one horizontal period.
The timing controller 50 generates the data control signal DCS and the scan control signal SCS corresponding to an external synchronization signal. The data control signal DCS and the scan control signal SCS are supplied from the timing controller 50 to the data driver 20 and the scan driver 10, respectively. Further, the timing controller 50 rearranges external data and supplies it to the data driver 20.
The pixel portion 30 receives first power ELVDD and second power ELVSS from an external power source, and supplies them to the respective pixels 40. When the first power ELVDD and the second power ELVSS are applied to the pixels 40, each pixel 40 displays an image corresponding to the received data signal. Here, emission time of each pixel 40 is controlled corresponding to the emission control signal.
Like the scan signals, the emission control signals are supplied to the 1st through nth emission control lines En, in sequence. Here, every pixel 40 included in the pixel portion 30 does not emit light for a short time while the emission control signal is not supplied.
However, the first power ELVDD applied to the pixel portion 30 varies according to how many pixels 40 emit light, i.e., according to a pattern and brightness of an image displayed on the pixel portion 30. That is, the first power ELVDD supplied per frame is differently loaded to the pixels 40 according to how many pixels 40 emit light. For example, when relatively many pixels 40 emit light during one frame, the relatively high first power ELVDD is loaded to the pixels 40. On the other hand, when relatively small pixels 40 emit light during one frame, the relatively low first power ELVDD is loaded to the pixels 40. Therefore, voltage difference corresponding to the pattern of an image arises between the pixels 40 receiving the first power ELVDD 40, and thus there is a problem in that the image is displayed with non-uniform brightness. Further, due to voltage drop, the voltage of the first power ELVDD is differently applied to the pixels 40 according to the positions of the pixels 40 formed in the pixel portion 30, and thus the image is displayed with non-uniform brightness.